With the rapid proliferation of radio LAN apparatuses typified by IEEE802.11b apparatuses, a society is envisioned in which a seamless network is established through the mutual radio connection of audiovisual devices and/or personal computers, and the establishment of a technologies that realize small, high-speed data communication apparatuses inexpensively has become a matter of urgency.
Pulse radio communication using a pulse-shaped modulated signal has attracted attention as one such technology. As a conventional method of synchronizing a receive data signal in a pulse radio communication apparatus, a method is known whereby synchronization is performed by means of correlation between a reference time and preceding and succeeding signals for which delay processing is executed (see Patent Document 1, for example).
FIG. 12 is a block diagram showing the configuration of a conventional pulse radio communication apparatus described in Patent Document 1. In FIG. 12, a conventional pulse radio communication apparatus 1200 is composed of an amplifier 1202 that amplifies an RF signal received by an antenna 1201, a filter 1203 that eliminates an unwanted signal, an analog coding section 1204 that analogizes a signal, a splitter 1205 that splits a signal, a plurality of delay devices 1206, 1207, and 1208 that delay signals, a plurality of multipliers 1209, 1210, and 1211 that multiply signals, a plurality of integrators 1212, 1213, and 1214 that perform time integration, a reception synchronization control section 1217 that performs synchronization determination and delay control according to a correlation, a phase delay section 1218 that delays the phase of a signal, a main received wavelet code generator 1216 that modulates a phase-delayed signal and performs spreading with the same spreading code, and a splitter 1215 that splits main received wavelet code generator 1216 output into three, and outputs the three split signals to multipliers 1209, 1210, and 1211.
With this configuration, a received RF signal is amplified to an amplitude necessary for demodulation by amplifier 1202, an out-of-band unwanted frequency band is eliminated by filter 1203, and an analog signal is generated by analog coding section 1204. This signal is split by splitter 1205, and three delayed signals—namely, a signal delayed by time L, a signal delayed by time L+Y, and a signal delayed by time L−Y—are output by delay devices 1206, 1207, and 1208. These three signals are multiplied by multipliers 1209, 1210, and 1211 respectively by a reference pulse signal generated by main received wavelet code generator 1216, and undergo time integration corresponding to the respective symbols by integrators 1212, 1213, and 1214. Synchronization is determined and phase delay section 1218 is controlled by reception synchronization control section 1217 according to the correlations of the signals, and decoded data 1219 is output while sliding synchronization is performed. At this time, adjustment is performed to synchronize with the transmit data signal by having the tracking cycle delayed by phase delay section 1218 if the correlation of the time L+Y signal is higher than that of the time L signal, taking the time L reception path signal as a correlation reference, and conversely, having the tracking cycle advanced by phase delay section 1218 if the correlation of the time L−Y signal is higher. Patent Document 1: National Publication of International Patent Application No. 2003-535552 (paragraph 148, FIG. 27).